Wooed by the fractured nature of the Republican primary and the huge news media presence in this state, Mr. Romney is now aggressively betting that a victory here will accelerate his drive to the nomination. The outcome of that bet will be known in five days.

Mr. Romney is courting supporters in the northern part of Iowa today before making a brief 36-hour jaunt to New Hampshire, where his campaign strategy has always been firmly rooted. After a spaghetti dinner in Merrimack, N.H., and a breakfast in Hampton, Mr. Romney will dash back to Iowa on Saturday for the final push before Tuesday’s voting.

“This is an exciting time,” Mr. Romney told an overflow crowd in Clinton, Iowa, Wednesday evening. “We’re going to take back the White House, thanks to you guys.”

Mr. Romney’s aides continue to play down expectations of a first-place showing in Iowa. Recent polls in the state show the former Massachusetts governor is effectively tied with Representative Ron Paul of Texas for the lead here. But the fickle nature of the Republican electorate over the past several months keeps the possibility of a surprise alive.

Mr. Romney arrived in Mason City shortly after lunchtime on Thursday and was met by a crowd of a few hundred people who gathered at Music Man Square. His mood was upbeat and his smile was wide.

“Sure I want to win Iowa, everyone wants to win Iowa,” Mr. Romney said, gently prodding Republicans to carefully study the field of candidates. He added: “Who do you think can beat Barack Obama? Look at the candidates, decide who you like and see who you think could become president.”

On Wednesday Mr. Romney acknowledged that his campaign’s new push in Iowa has changed expectations. Asked whether a second-place finish behind Mr. Paul would qualify as a victory, Mr. Romney was quick to answer.

“Uh, no,” he said.

Aides to Mr. Romney said the campaign remains focused on collecting delegates over the long haul. A “super PAC” supporting Mr. Romney has already begun reserving airtime in South Carolina and Florida in anticipation of the fight to come later in January.

But in a sign of how much the campaign is betting on success in Iowa, Mr. Romney has decided to remain in the state until the morning after the caucuses, rather than heading out to New Hampshire early to get a jump on the weeklong stretch before voting there.

Asked on Wednesday whether there was a reason he might not win the caucuses, Mr. Romney said: “I can’t imagine. Except there are other good people running. And they’ve got good campaigns.”

One of his rivals, Representative Michele Bachmann, was struggling to explain the abrupt departure of her Iowa chairman to Mr. Paul’s campaign. Kent Sorenson, a prominent state senator in Iowa and one of her top advisers, appeared at an event for Mr. Paul on Wednesday night and announced that he had switched his allegiance.

At a news conference Thursday morning, Mrs. Bachmann said Mr. Sorenson had told her Mr. Paul’s campaign had offered him money to switch, an accusation vehemently denied by Mr. Paul’s campaign.

“He told me that he was offered money,” Mrs. Bachmann said. “He was offered a lot of money by the Ron Paul campaign to go and associate with the Ron Paul campaign. She said the conversation took place over the phone on Tuesday.

Adding to the sense of confusion surrounding Mr. Sorenson’s departure, another top Bachmann aide — Wes Enos, her own political director in Iowa — disputed Mrs. Bachmann’s assertion.

“I can say unequivocally that Kent Sorenson’s decision was in no way financially motivated,” Mr. Enos said.

His statement was distributed by Mr. Paul’s campaign. Asked whether Mr. Enos was still part of Mrs. Bachmann’s campaign, an aide to Mrs. Bachmann said he could not update his status.

Other Republican candidates continued their push on Thursday in unseasonably warm weather for December in Iowa.

Rick Santorum, whose third-place standing in a recent CNN/Time Magazine poll has given his campaign new confidence, met with supporters in Coralville, Iowa Thursday morning.

Mr. Santorum had to practically fight his way through a crush of cameras and reporters on his way out of his “Faith, Family and Freedom” town hall. In his remarks, as he fielded a variety of questions on subjects like small business investment and immigration reform, he took the occasion of his sudden rise in the polls to make a swipe at the national media, which have mostly overlooked his campaign.

“Rick you’re so back in the polls. When are you going to get your boom? When are you going to get your bump?” he said, paraphrasing a question he said he was asked all the time. “I’ll get that bump on Jan. 3,” he said. “It’s not going to be created by the media. It’s not going to be created by a clever slogan or a glib performance in a debate. It’s going to be based on people looking at all the candidates and making a decision about who they believe is the best person to step forward.”

Ron Paul headed west toward Council Bluffs on Thursday as his campaign was lifted by polls showing him near the top of the field. Hundreds of supporters gathered for a rally for Mr. Paul in Des Moines Wednesday night in advance of several town hall meetings today.

Rick Perry is spending Thursday traveling across the north and east, pressing his case for being the outsider in the race. At every stop, Mr. Perry argues for his proposal to make Congress a part-time legislature.

Mr. Perry called Mr. Santorum a “prolific earmarker” on Thursday, a charge that he has made in a radio ad this week.

“Rick Santorum is proud of feeding at the earmark trough in Congress,” Mr. Perry’s ad says.

President Obama drew criticism on Thursday when he said, “we don’t have a strategy yet,” for military action against ISIS in Syria. Lawmakers will weigh in on Mr. Obama’s comments on the Sunday shows.Read more…